Automatically switched optical network and method for data transmission in the network

ABSTRACT

An automatically switched optical network includes several areas of a transmission plane and a control plane, and a method for data transmission in the network includes that when the control plane has detected at least one partition of an area separated from other partitions of the area, a route over area is realized between the separated partitions of the area by the way of virtual link in the area. When several partitions exist in a certain area of the network, which can not be connected with each other through routes within the area, and the data transmission can not be performed between these partitions, a hierarchical route in the case of the area of ASON transmission plane being parted is realized by the method, so when the several separated partitions are caused by link fault in a certain area, the hierarchical route over area can be realized for the partitions of the area.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national phase of PCT Appln. No.PCT/CN2007/071111filed Nov. 21, 2007, the disclosure of which isincorporated in its entirety by reference herein.

TECHNICAL FIELD

The present invention relates to the field of optical communication, andmore particularly, to an automatically switched optical network and amethod for transmitting data in the network.

TECHNICAL BACKGROUND

In the prior art, in section 6.2 of the G.8080 standard of the ITU-T forITU Telecommunication Standardization Sector (ITU-T), an automaticallyswitched optical network (ASON) transport plane is divided into routingareas and subnets, where one routing area may be composed of a number ofsub-areas or subnets. The function of hierarchical routing may beimplemented on the ASON transport plane by dividing routing areas. TheG.17715 standard describes systematically the implementation of thehierarchical routing, the main idea of which is to convert the routebetween a pair of nodes belonging to different areas respectively intohierarchical routes. As shown in FIG. 1, the route from a node A in anarea 1 to a node B in an area 4 is divided into an intra-area route fromthe node A to the boundary of the area 1, an inter-area route from thearea 1 to the area 4 and an intra-area route from the boundary of thearea 4 to the node B. In this figure, the intra-area route is indicatedby a thin line and the inter-area route is indicated by a thick line.Thus, route-finding of a cross-area connection can be implemented by theinter-area route provided by a node on the boundary of the area 1 andthe intra-area route to the node B provided by a node on the boundary ofthe area 4 on the other side, provided that the node A has the route tothe boundary of the area 1.

Therefore, the advantage of dividing areas is that details of networktopology outside the areas can be shielded, each area is only requiredto maintain its own internal network topology, and by link aggregation,connections between the areas are maintained and inter-area routes aregenerated, thereby decreasing the consumption of the CPU of a ASON nodein calculating topology routes and increasing the convergence speed ofthe network.

The concept of area hierarchical routing of the ASON transport plane ismentioned in both the G.67715 standard and the G.8080 standard, butneither of the standards involves a reference to a partitioned area. Infact, the area hierarchical routing of the ASON transport plane issimilar to the area routing aggregation theory of the Open Shortest PathFirst (OSPF) standard routing protocol. The OSPF standard protocolRFC2328 discusses specially the concept of a partitioned area in section3.7 “Partitions of areas”, and provides measures to solve the problem ofpartitioned area connectivity. It is discovered by comparison that forthe area hierarchical routing theory of the ASON transport plane, it isnecessary to consider an implementation method of the hierarchicalrouting in the case of a partitioned area.

SUMMARY OF THE INVENTION

A technical problem to be solved by the present invention is to providean automatically switched optical network and a method for transmittingdata in the network, such that when some area in the network has someportions that can not be connected with one another by an intra-arearoute, connectivity among these portions can be achieved.

In order to solve the above technical problem, the present inventionprovides an automatically switched optical network, comprising: a numberof areas on a transport plane, and a control plane, wherein,

at least one portion of an area is isolated from the other portions ofthe area, then the area is a partitioned area and each portion of thepartitioned area is a partition of the area; and

the control plane is configured to realize a cross-area route betweenthe isolated partitions of the area by a virtual link.

Furthermore, the control plane realizes a cross-area route between theisolated partitions of the area by the virtual link means:

when the control plane detects that an area has become a partitionedarea due to a link failure, the control plane configures a virtual linkat an boundary of each partition of the area respectively, sets up asoft permanent connection (SPC) service connection between a node in anyone partition of the area and another node in any other partition of thearea, and obtains a route between the nodes in the two partitions of thearea through the virtual link.

Furthermore, service data carried by the SPC service connection betweenthe nodes in the two partitions of the area is transmitted transparentlyover the virtual link passed.

Furthermore, the route between the nodes in the two partitions of thearea is logically an intra-area route, but physically crosses a numberof areas.

Furthermore, the at least one portion of an area being isolated from theother portions of the area means:

the at least one portion of the area can not be connected with the otherportions of the area by an intra-area route.

The present invention also provides a method for transmitting data in anautomatically switched optical network, applied for data transmissionamong a number of portions of an area in the network when the portionsare isolated from one other, each of the portions being referred to as apartition of the area; the method comprising:

when a control plane detects that at least one portion of an area isisolated from the other portions of the area, realizing a cross-arearoute between the isolated partitions of the area by a virtual link.

Furthermore, realizing a cross-area route between the isolatedpartitions of the area by the virtual link means:

the control plane configuring a virtual link at an boundary of eachpartition of the area, setting up a soft permanent connection (SPC)service connection between nodes in any two partitions of the area whendata needs to be transmitted between the nodes in the two partitions ofthe area, and obtaining a route between the nodes in the two partitionsof the area through the virtual link.

Furthermore, the route between the nodes in the two partitions of thearea is logically an intra-area route, but physically crosses a numberof areas.

Furthermore, the method further comprises:

transmitting service data carried by the SPC service connection betweenthe nodes in the two partitions of the area transparently over thevirtual link passed.

Furthermore, the portions being isolated from one other means that theportions can not be connected with one another by an intra-area route.

The technique scheme of the present invention provides a method forimplementing hierarchical routing in the case of a partitioned area onthe ASON transport plane, such that when some portions of an area cannot be connected with one another by an intra-area route due to a linkfailure in the area, cross-area hierarchical routing of the partitionedarea can be implemented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of cross-area hierarchical routing in theprior art;

FIG. 2 is a flow chart of a specific embodiment of a method fortransmitting data in an automatically switched optical network inaccordance with the present invention;

FIG. 3( a) and (b) are schematic diagrams of partitioned area scenariosin an application example of the present invention; and

FIG. 4 is a schematic diagram of a virtual link between partitionedareas in an application example of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

The technical scheme of the present invention will be described indetail below in conjunction with the accompanying drawings andembodiments.

The present invention provides an automatically switched optical network(ASON) including a number of areas. When at least one portion of an areais isolated from the other portions of the area due to a link failureinside the area, the area becomes a partitioned area of which eachportion is referred to as a partition of the area; and the control planeis used to realize a cross-area route between the isolated partitions ofthe area by a virtual link.

The concept of a partitioned area of the ASON transport plane ispresented first in the present invention. The partitioned area refers toan area of which at least one portion is isolated from the otherportions due to a link failure inside the area, the at least one portionof the area being isolated from the other portions means that the atleast one portion of the area can not be connected with the otherportions by an intra-area route. If an area becomes a partitioned areaand any partition of the area can be reconnected with one anotherthrough other areas, then in theory connections can still be set up andcommunications can be kept between nodes or subnets in the partitions ofthe area, except that in this partitioned area, a service connectionfrom one partition of the area to another is physically no longer anintra-area path but has to be realized with an inter-area path.

The present invention further presents a method for realizing across-area route between nodes in partitions of a partitioned area by avirtual link. When the control plane detects in real time that an areahas become a partitioned area due to a link failure, a passage betweenany partition of the area and any other partition of the area can beformed logically by configuring a virtual link at the boundary of eachpartition of the partitioned area respectively; thus, the transportplane topology between the two partitions of the area can be shielded bythe virtual link passage between them, thereby achieving the directconnection between them. In such a case, a soft permanent connection(SPC) service connection between nodes in the two partitions of the areais set up to obtain a route between the nodes in the two partitions ofthe area through the virtual link. The obtained route is logically stillan intra-area route, the two ends of the virtual link are considered tobe adjacent nodes, and service data carried by the SPC serviceconnection will be transmitted transparently over the virtual linkpassed.

The present invention further provides a method for transmitting data inthe ASON, applied for data transmission between some portions of an areain the network—the portions are isolated from one another, i.e., theportions can not be connected by an intra-area route—namely datatransmission between partitions of a partitioned area; the partitionedarea refers to an area of which at least one portion is isolated fromthe other portions due to a link failure inside the area; each portionof the partitioned area is referred to as a partition of the area.

The method is shown in FIG. 2 and comprises the following steps:

A. The control plane detects in real time that an area has become apartitioned area.

In this step, the control plane detects in real time that an area hasbecome a partitioned area means that the control plane detects in realtime that at least one portion of an area is isolated from the otherportions of the area due to a link failure.

B. The control plane configures a virtual link at the boundary of eachpartition of the area respectively. By this step, a passage between anypartition of the area and any other partition of the area is formedlogically.

C. When data needs to be transmitted between nodes in any two partitionsof the area in the partitioned network, a SPC service connection betweenthe nodes in the two partitions of the area is set up, and a routebetween the nodes in the two partitions of the area is obtained throughthe virtual link.

D. Service data carried by the SPC service connection between the nodesin the two partitions of the area is transmitted transparently over thevirtual link passed.

The prevent invention will be further described in conjunction with anapplication example.

As shown in FIG. 3( a), area RA-1, area RA-2 and area RA-3 are threetransport areas independent of one another. The area RA-1 consists oftwo portions: RA-1.1 and RA-1.2, which are connected by a subnet nodepoint (SNP) link connection A in a unique subnet node point group (SNPP)link 1. At the meantime, RA-1.1 and RA-2 are connected by a SNP linkconnection B in a SNPP link 2, RA-1.2 and RA-3 are connected by a SNPlink connection C in a SNPP link 3, and RA-2 and RA-3 are connected by aSNP link connection D in a SNPP link 4.

When failure occurs in the link 1, the area RA-1 is partitioned into twoportions: RA-1.1 and RA-1.2, and as shown in FIG. 3( b), at this time,the two partitions of the area are still kept connected physically bythe areas RA-2 and RA-3. However, because both RA-1.1 and RA-1.2 belongto the area RA-1, the connection route between a node in RA-1.1 and anode in RA-1.2 is always considered to be an intra-area route. Accordingto the discussion of hierarchical routing in G.8080 and G.7715 in theprior art, the route between the nodes in RA-1.1 and RA-1.2 will neverbe acquired by an inter-area route.

In regard to this situation, the present invention presents a method forrealizing a cross-area route between nodes in RA-1.1 and RA-1.2 by avirtual link. When the control plane detects in real time that thesituation shown in FIG. 3( b) takes place, a passage between RA-1.1 andRA-1.2 can be formed logically by configuring a virtual link atboundaries of RA-1.1 and RA-1.2 respectively. As shown in FIG. 4, thevirtual link is indicated by a dashed line and the virtual link includesthe SNP link connection B between RA-1.1 and RA-2, the SNP linkconnection D between RA-2 and RA-3 and the SNP link connection C betweenRA-1.2 and RA-3. Thus, the transport plane topology between RA-1.1 andRA-1.2 can be shielded by the virtual link passage, thereby realizing adirect connection between them.

In such a case, a soft permanent connection (SPC) service connectionbetween the nodes in RA-1.1 and RA-1.2 is set up to obtain a routethrough the virtual link. The obtained route is logically still anintra-area route, the two ends of the virtual link are considered to beadjacent nodes, and the service carried by the connection will betransmitted transparently over the virtual link passed.

Specific implementation of the virtual link may depend on the transportdevice used in practice. Common methods include transmitting a servicedirectly and transparently by a tunnel, setting up a dedicated permanentconnection (PC) or SPC connection between the two ends of the virtuallink to realize the virtual link passage, etc., which will not beenumerated herein.

Of course, various other embodiments in accordance with the presentinvention may be used. Those skilled in the art may make variouscorresponding modifications and variations according to the presentinvention, without departing from the spirit and essence of the presentinvention. All such corresponding modifications and variations shallfall into the protection scope defined by the appended claims.

Industrial Applicability

The technique scheme of the present invention provides a solution to theproblem that data can not be transmitted between some portions of anarea in a network when these portions can not be connected with oneanother by an intra-area route, and provides a method for implementinghierarchical routing in the case of a partitioned area on the ASONtransport plane such that when an area has some portions that areisolated from one another due to a link failure therein, cross-areahierarchical routing of the partitioned area can be implemented.

What we claim is:
 1. An automatically switched optical network,comprising: a number of areas on a transport plane, and a control plane,wherein, at least one portion of an area is isolated from the otherportions of the area, where the area is referred to as a partitionedarea and each portion of the partitioned area is referred to as apartition of the area; and the control plane is configured to realize across-area route between the isolated partitions of the area by avirtual link; wherein the control plane realizes a cross-area routebetween the isolated partitions of the area by the virtual link means:when the control plane detects that an area has become a partitionedarea due to a link failure, the control plane configures a virtual linkat an boundary of each partition of the area respectively, sets up asoft permanent connection (SPC) service connection between a node in anyone partition of the area and another node in any other partition of thearea, and obtains a route between the nodes in the two partitions of thearea through the virtual link.
 2. The automatically switched opticalnetwork according to claim 1, wherein service data carried by the SPCservice connection between the nodes in the two partitions of the areais transmitted transparently over the virtual link passed.
 3. Theautomatically switched optical network according to claim 1, wherein theroute between the nodes in the two partitions of the area is logicallyan intra-area route, but physically crosses a number of areas.
 4. Theautomatically switched optical network according to claim 1, wherein theat least one portion of an area being isolated from the other portionsof the area means: the at least one portion of the area can not beconnected with the other portions of the area by an intra-area route. 5.A method for transmitting data in an automatically switched opticalnetwork, applied for data transmission among a number of portions of anarea in the network when the portions are isolated from one other, eachof the portions being referred to as a partition of the area; the methodcomprising: when a control plane detects that at least one portion of anarea is isolated from the other portions of the area, realizing across-area route between the isolated partitions of the area by avirtual link; wherein realizing a cross-area route between the isolatedpartitions of the area by the virtual link means: the control planeconfiguring a virtual link at an boundary of each partition of the area,setting up a soft permanent connection (SPC) service connection betweennodes in any two partitions of the area when data needs to betransmitted between the nodes in the two partitions of the area, andobtaining a route between the nodes in the two partitions of the areathrough the virtual link.
 6. The method according to claim 5, whereinthe route between the nodes in the two partitions of the area islogically an intra-area route, but physically crosses a number of areas.7. The method according to claim 5, further comprising: transmittingservice data carried by the SPC service connection between the nodes inthe two partitions of the area transparently over the virtual linkpassed.
 8. The method according to claim 5, wherein the portions beingisolated from one other means that the portions can not be connectedwith one another by an intra-area route.